No exploitation reportedFix available

CVE-2021-3909

Q: Is CVE-2021-3909 actively exploited?

Active exploitation of CVE-2021-3909 has not been confirmed. Its EPSS score was 1.6% on 2026-10-22, the estimated probability of exploitation in the next 30 days.

Q: What is the CVSS score for CVE-2021-3909?

CVE-2021-3909 has a CVSS v3 base score of 7.5 (HIGH severity), with vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H.

No exploitation reported by the sources we read.

Published2021-11-11
Fixed in1.3.0
WeaknessCWE-400

Am I affected?

With a domain, we read the version its public headers and pages expose. A distribution build can carry the fix under an older number.

Description

OctoRPKI does not limit the length of a connection, allowing for a slowloris DOS attack to take place which makes OctoRPKI wait forever. Specifically, the repository that OctoRPKI sends HTTP requests to will keep the connection open for a day before a response is returned, but does keep drip feeding new bytes to keep the connection alive.

Timeline

dates in UTC

2021-11-1122:15CVE publishedNVD

Observed activity

isMalicious corpus · updated 2026-10-23 18:48 UTC

Indicators tagged with this CVE, per day0 indicators over 7 days

Block these indicators

Firewall list (EDL, text): https://api.ismalicious.com/edl/cve/CVE-2021-3909?format=txt
CSV export: https://api.ismalicious.com/edl/cve/CVE-2021-3909?format=csv
TAXII collection of exploited CVEs
The EDL and CSV take an API key on the Pro plan.

Versions per branch

NVD

Cloudflare octorpki

Branch	Affected	Fixed in	Source
1.3	< 1.3.0	1.3.0	NVD

Debian debian linux

Branch	Affected	Fixed in	Source
11.0	= 11.0	no fix published	NVD

as publishedRanges as NVD and OSV publish them; a distribution’s build can be fixed under an older number.

Fix

Update Cloudflare octorpki to 1.3.0

Detection

Nuclei template: none so far
Exploit-DB: no entry
Proof-of-concept repositories: none listed

Sources

CNACVSS 3.14.4read 2026-10-23
NVDCVSS 3.17.5read 2026-10-23
NVDCVSS 2.05read 2026-10-23
CNAweakness (CWE)CWE-400read 2026-10-23
NVDweakness (CWE)CWE-400read 2026-10-23
FIRST EPSSEPSS score1.6 %2026-10-22

Technical details

CVSS v3 Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Published: 2021-11-11
Last Modified: 2026-06-17
NVD status: Modified

Frequently asked questions

What is CVE-2021-3909?

Is CVE-2021-3909 actively exploited?

Active exploitation of CVE-2021-3909 has not been confirmed. Its EPSS score was 1.6% on 2026-10-22, the estimated probability of exploitation in the next 30 days.

What is the CVSS score for CVE-2021-3909?

CVE-2021-3909 has a CVSS v3 base score of 7.5 (HIGH severity), with vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H.

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